1. Field of the Invention
The present invention relates in general to rotary vane pumps such as engine fuel pumps and actuator pumps and relates in particular to such pumps which vary their discharge flow by controllably metering the filling action of a fluid during the intake portion of vane cavity rotation.
2. Description of Prior Developments
Variable displacement pumps are typically more efficient than fixed displacement pumps controlled by bypass valves. Unfortunately, inefficiencies associated with prior variable displacement pumps have caused heating of the fluid as it is being pumped. Such heating is unacceptable in many advanced engine control systems such as those used in aircraft applications.
Although variable displacement piston pumps are commonly used in engine and aircraft hydraulic systems, vane pumps are generally more desirable for fuel applications since they are more contamination tolerant. Variable displacement vane fuel pumps generally require moving a cam to vary the pump displacement but this causes complexity in pump design and produces losses due to considerable leakage.
Accordingly, a need exists for an efficient, low loss, low leakage, variable delivery, positive displacement pump which embodies a relatively simple design.
A further need exists for a fuel pump of the variable delivery vane variety which is resistant to leakage and which does not require the use of a moving cam for varying the pump displacement or pump discharge flow.